The human eye functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors, including the size and shape of the eye and the transparency of the cornea and the lens. When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL).
In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During a phacoemulsification procedure, a probe tip of a phacoemulsification hand piece is inserted into the anterior segment of the eye through a small incision in the outer tissue of the eye. A user, such as a surgeon, brings the tip of the probe into contact with the lens of the eye, so that the vibrating tip fragments the lens. The resulting fragments are aspirated out of the eye through the interior lumen of the probe, along with irrigation solution provided to the eye during the procedure.
Throughout the procedure, irrigation fluid is introduced into the eye. This irrigation fluid prevents the collapse of the eye during the removal of the emulsified lens. The irrigation fluid also protects the eye tissues from the heat generated by the vibrating of the ultrasonic cutting needle. Furthermore, the irrigation fluid suspends the fragments of the emulsified lens for aspiration from the eye.
A problem that occurs during the phacoemulsification process arises from a blockage, or occlusion, of the probe's lumen. As the irrigation fluid and emulsified tissue is aspirated away from the interior of the eye through the probe's lumen, pieces of tissue that are larger than the diameter of the lumen or harder pieces of tissue may become lodged in the probe, obstructing flow therethrough. While the probe is clogged, pressure drops (i.e., vacuum builds). When the material within the needle becomes dislodges, a rapid pressure change occurs within the anterior chamber of the eye results. This rapid pressure change can result in aspiration of a relatively large quantity of fluid and tissue out of the eye very quickly and is referred to as post-occlusion surge. This post-occlusion surge can, in some cases, cause injury to the eye, such as, causing the eye to collapse and/or causing the lens capsule to be torn.